feat: external importers + uptime monitors (merge plan M1)

Two tracks from the Beszel/Domain-Locker merge plan in ROADMAP.md:

- Importers: POST /api/import/external sniffs Homepage services.yml,
  Homarr JSON, and Dashy conf.yml into sections/items; SettingsDialog
  import now accepts all four formats.
- Monitors (M1): monitors + heartbeats schema, pure checkers for
  http/tcp/ping/dns/keyword/json-query/push, scheduler on app ctx,
  CRUD + check-now + push ingest API, /monitors + /monitors/:id pages
  (wouter), monitor board widget, ServiceDialog monitor opt-in.

Authored By: TDvorak <[email protected]>

Generated with Devin (https://devin.ai)

Co-Authored-By: Devin <158243242+devin-ai-integration[bot]@users.noreply.github.com>

apps/frontend/src/widgets/monitor.tsx

@@ -0,0 +1,38 @@
+import type { WidgetData } from "@/widgets";
+import type { Item } from "@/types";
+import { cn } from "@/lib/utils";
+
+// Board tile for an uptime monitor: status dot, uptime %, avg ping.
+// config.monitorId binds it; data comes from the monitor fetcher.
+export function MonitorWidget({ item, data, error }: {
+	item: Item;
+	data: WidgetData | undefined;
+	error: string | undefined;
+}) {
+	const status = typeof data?.status === "string" ? data.status : undefined;
+	const uptime = typeof data?.uptime24 === "number" ? data.uptime24 : undefined;
+	const ping = typeof data?.ping === "number" ? data.ping : undefined;
+	const monId = typeof item.config?.monitorId === "string" ? item.config.monitorId : "";
+
+	return (
+		<a
+			href={monId ? `/monitors/${monId}` : "/monitors"}
+			className="flex w-full items-center gap-2.5 text-left"
+			onClick={(e) => e.stopPropagation()}
+		>
+			<span
+				className={cn(
+					"size-1.5 shrink-0 rounded-full",
+					error ? "bg-down" : status === "up" ? "bg-up" : status === "down" ? "bg-down" : "bg-text-faint/40",
+				)}
+			/>
+			<span className="min-w-0 flex-1 truncate text-[12.5px] font-medium">
+				{typeof data?.name === "string" ? data.name : item.name}
+			</span>
+			<span className="shrink-0 font-mono text-[10.5px] text-text-faint">
+				{error ? "err" : uptime !== undefined ? `${uptime.toFixed(1)}%` : "…"}
+				{ping ? ` · ${Math.round(ping)}ms` : ""}
+			</span>
+		</a>
+	);
+}